Native form of endothelin receptor in human placental membranes

Little is known about the native form of endothelin receptor. To clarify its functional and structural properties, we solubilized the receptor from human placenta in an active form using mild detergents CHAPS and digitonin and showed that it is able to bind 125I-endothelin-1 in a specific manner, with a pH optimum between 6 and 8 in contrast to a reported pH optimum of 4. The molecular weight of the receptor was estimated as 340,000 by gel filtration of the solubilized membrane in the presence of 0.2% (w/v) digitonin. When the solubilized membranes were labeled with 125I-endothelin-1 prior to gel filtration, the radioactive ligand also migrated in the position corresponding to a 340 kDa protein. These results indicated that the native form of endothelin receptor in human placenta is a 340 kDa protein.